1. Field of the Invention
The present invention relates to a digital teleconverter.
2. Description of the Related Art
A filming device or a shooting device such as a video camera comprises a digital image processor which processes an image information transmitted from the camera by way of digital signals. There are two kinds of such a digital image processor. One is a type in which a composite signal is used. The composite signal is a compound of a luminance signal and a chrominance signal. The other is a type in which component signals such as the luminance signal and the chrominance signal are individually used.
With respect to the composite signal using type image processing system, the circuit for processing the signal is simple and it is unnecessary to prepare a digital memory having a large storage capacity. For example, in accordance with this system, it is possible to directly storage the video signal of NTSC (National Television System Committee) system along with a synchronizing signal in a digital memory device after converting the analogue video signal to a digital signal. Also, it is possible, vice versa, to obtain an NTSC video signal by reading the video information data storaged in the digital memory device and converting the digital data to an analogue signal. Therefore, it becomes possible to directly connect the system to the television system and directly interchange the video signals therebetween. However, the functions of the image processing system of this type are limited so that the system is only capable of carrying out the still filming operation or the stroboscopic filming operation.
On the other hand, with respect to the component signal using type image processing system, it becomes possible to widening the function of the system so that the system is capable of carrying out various functions in addition to the still function and the stroboscopic function. However, the structure of the processing system of this type is very complicated. Besides, it is necessary to prepare a digital memory device having a large storage capacity. For example, when the NTSC video signal is to be used, it is necessary to prepare a selector circuit for separating the luminance signal (Y) and the chrominance signal (C) from each other and a demodulation circuit for demodulating the signals (Y) and (C). Further, it is necessary to prepare and arrange an A/D converter for each of the luninance signal and the chrominance signal. Also, a D/A converter and an NTSC encoder have to be interposed between the system and the television system to transmit the video information data read from the digital memory device to the television. Further, a large amount of power is consumed by the A/D converter since it is necessary to drive the converter at a high speed. Therefore, it is requied to reduce the number of the A/D converters used in the processing system from the stand point of energy consumption.